CDX
Readablearchive
A CDX file consists of individual lines of text, each of which summarizes a single web document. The first line in the file is a legend for interpreting the data, and the following lines contain the data for referencing the corresponding pages within the host. The CDX signatures use a field delimiter character which is assumed to be a space character, however please contact the PRONOM team should you encounter CDX index files where the delimiter is different.
Identify it
| Extensions | .cdx |
|---|---|
| MIME types | text/plain |
| Signatures | 2043445820 at byte 0 (CDX Archive Index variant 1)43445820 at byte 0 (CDX Archive Index variant 2) |
| PRONOM | fmt/869 |
| Wikidata | Q47538013 |
| Library of Congress | fdd000590 |
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From Just Solve the File Format Problem (File Formats Wiki), PRONOM, Wikidata. Updated 2026-10-24.